Definition: Stellar Classification: Stars given a designation consisting of a letter and a number according to the nature of their spectral lines which corresponds roughly to surface temperature. The classes are: O, B, A, F, G, K, and M; O stars are the hottest; M the coolest. The numbers are simply subdivisions of the major classes. The classes are oddly sequenced because they were assigned long ago before we understood their relationship to temperature. O and B stars are rare but very bright; M stars are numerous but dim. The Sun is designated G2.
Temperature
- O: 30,000 - 60,000 K: Blue stars
- B: 10,000 - 30,000 K: Blue-white stars
- A: 7,500 - 10,000 K: White stars
- F: 6,000 - 7,500 K: Yellow-white stars
- G: 5,000 - 6,000 K: Yellow stars (like the Sun)
- K: 3,500 - 5,000K: Yellow-orange stars
- M: < 3,500 K: Red stars